This invention relates to methods for deploying cable in a body of water. This invention is especially useful for deploying temporary fiber optic cables and cables with integral sensors, known as sensor arrays, in an ocean.
Sensor arrays are usually deployed from surface ships which release the cable from a cable storage device such as a spool and allow the sensor arrays to sink to a desired location. In a desire for covertness, it has been suggested to deploy large arrays and cables from submarines through a torpedo hatch, but this requires very complex and expensive installations that reduce the submarine war fighting capabilities and have been very difficult, if not impossible to implement successfully.
The use of surface ship systems to deploy sensor arrays is cumbersome, expensive, and manpower intensive. There are also difficulties encountered when trying to connect several legs of arrays in a star pattern to a central connection point, a necessary deployment style for several applications. Problems are also encountered when trying to deploy multiple arrays connected to a central umbilical cable. In both of these cases the surface ship needs to lay a track over each individual leg of the cables and arrays. In addition, they must be interconnected at a common connection point after the lay is completed, a very difficult task, especially in deep water. For some time there has been a desire to find a more efficient, effective, flexible and economical means for laying sensor arrays in a body of water.
It is therefore an object of the present invention to provide an improved method for deploying cables and arrays in a body of water effectively and efficiently.
This object, and others which will become apparent from the following disclosure, are achieved by the present invention which comprises in one aspect a method for deploying cable in a body of water comprising providing an autonomous underwater vehicle (AUV) capable of converting vertical motion into horizontal travel, having a housing for storing cable and adapted to release cable in the body of water, and placing the cable in the body of water with the AUV.
AUVs that use buoyancy as a means of propulsion are commonly known as sea gliders, and these two terms are used interchangeably. Sea gliders have wings which are used to develop lift with a component of force in the horizontal direction that drives the vehicle forward. Several relatively small sea gliders have been built and used for oceanographic research, but no one has heretofore suggested using sea gliders for deploying cable.
One embodiment of the method of the invention employs AUVs that are relatively inexpensive and expendable and thus can be used as anchors for the deployed cable. The method uses sea gliders that include a housing for storing and release of the cable and array with the housing and release system, preferably on the stem or aft portion of the AUV.
One embodiment of the method of this invention uses sea gliders that have constant negative net buoyancy, in which case the sinking of the AUV from the surface of the water is used to develop the glide having the horizontal vector. In another embodiment the buoyancy is positive, in which case the AUV can be released from the bottom of the body of water and the rising to the surface used to develop a glide having a horizontal vector. In this embodiment, a simple flooding mechanism can be used to allow the sea glider to sink when it nears the surface (i.e. becomes negatively buoyant) for a doubling of the horizontal range. For much longer deployments, limited only by the size and power source of the sea glider, one of several methods can be used to cycle the net buoyancy between a positive and negative value, thereby causing the AUV to fall or rise in the body of water, and to convert the vertical motion in each direction into horizontal travel. Depending on the particular mission requirements, either fixed or controllable pitch wings can be utilized.
The sea glider can be dropped from the surface to begin the cable deployment, or released from a submarine through the torpedo hatch or, if size limitations for the particular mission dictate using a unit too large for torpedo tube launch, the AUV can be externally mounted and deployed. The sea glider can also be released from a weighted bunker, which has been placed on, or dropped, to the bottom of the body of water. At the end of the cable deployment, the AUV can act as an anchor for the cable. Similarly the bunker, if so used, acts as an anchor for the cable and/or array. The sea glider or the weighted bunker, if so used, can also house power, electronics, and or communications equipment associated with the particular array or cable deployed. Surface and/or sub-surface buoys and location devices can be deployed from any point(s) desired.
In the embodiments using a weighted bunker, one or more sea gliders can be housed within the weighted, negatively buoyant bunker which is dropped to or placed on the bottom of the water. When released from the bunker, each AUV rises and glides, releasing cable from the cable housing during the glide. For multiple legs from a central point, the individual cables and associated electronics can be connected within the bunker prior to deployment.
In deployment applications having a primary umbilical cable with array legs or spurs connected to it, the umbilical cable can be laid using a conventional surface ship with the individual legs deployed by dropping sea gliders from the surface vessel with the cable end prespliced into the primary umbilical cable. This permits the surface ship to run on the primary track only, saving time, track coverage, and eliminating the problem of connecting multiple cables after the arrays are laid.
One embodiment encompasses the use of sea gliders that have been adapted for submarine launch from torpedo or vertical launch tubes. Multiple legs can be deployed serially at the end point of the previous leg. In such cases, the AUV contains a locating device to assist the submarine in finding the AUV at the end point. In those cases where individual legs are laid, sub-surface buoys can be deployed at both ends for later mating. Alternatively, one end of the cable can be kept aboard the submarine for attachment between legs that begin in a common area (such as for star pattern deployments or double length legs). Depending on the particular mission, the submarine can keep the free end of a sea glider deployed cable and array and process data in real time.
Another series of embodiments provide one or more AUVs encapsulated and dropped from aircraft. A relatively simple sea glider configuration can be placed in a modified sonobuoy and dropped from a P3 type aircraft. The sonobuoy would house a small, heavy (i.e. negatively buoyant) sea glider that is released on water impact. A dead weight package with electronics, battery, and cable termination would drop vertically to the sea floor while the sea glider with the free end of the array travels horizontally, deploying the array and cable in a predetermined direction to the sea floor. A surface buoy with RF antenna would be deployed from the dead-weight package, either on impact, at a predetermined time, by later command, or automatically when a target is detected, for example. A vertical array can also be deployed from the dead-weight package on the bottom. In such case, a small subsurface buoy would hold the vertical array with the RF antenna supported from the subsurface buoy to provide a relatively stable vertical array devoid of the negative affects associated with the motion of the seas, as opposed to a surface suspended system that can have substantial undesired mobility, especially in a near-shore environment.
Sea glider alternating vertical motion can be provided by a subsystem which changes the buoyancy of the AUV. For example, compressed gas in combination with a blow valve, ballast tanks, and a programmed processor can be used to produce alternating flood and blow cycles, which cause the sea glider to cycle through sinking and floating, each motion being converted by the AUV into horizontal gliding travel. The sea glider buoyancy can also be provided by a power source such as a chemical gas generator or a mechanical pump which derives energy from any source, for example a battery, fuel cell, or any other known power source for conventional AUV power.
If acoustic stealth is also required for a unit with multiple glide cycles, the method of blowing and flooding can incorporate quiet orifice and valve systems which are conventional in some submarine applications.
If control of the center of buoyancy of the sea glider is needed because the array package is large compared to the size of the vehicle (i.e weight is lost and the center of gravity changes while cable is being deployed), control may be maintained by using strategically placed multiple tanks that can be flooded or blown individually as needed.
The track location of an array deployment can be measured, and if desired, controlled using existing AUV underwater navigation and control equipment. Alternatively, the sea glider can deploy a simple antenna to the surface at any point along the deployment track to get a Global Positioning System (GPS) fix and either use the information for repositioning or to log location.
These methods can be utilized in any body of water such as an ocean, sea, bay, river, harbor, or lake. There is no limit to the maximum depth this method can be used or the lengths of those deployments dependant on the AUV size, materials used, and power source available.